Task-space dynamic control of underwater robots

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Abstract

This thesis is concerned with the control aspects for underwater tasks performed by
marine robots. The mathematical models of an underwater vehicle and an underwater
vehicle with an onboard manipulator are discussed together with their associated
properties.
The task-space regulation problem for an underwater vehicle is addressed where the
desired target is commonly specified as a point. A new control technique is proposed
where the multiple targets are defined as sub-regions. A fuzzy technique is used to
handle these multiple sub-region criteria effectively. Due to the unknown gravitational
and buoyancy forces, an adaptive term is adopted in the proposed controller.
An extension to a region boundary-based control law is then proposed for an underwater
vehicle to illustrate the flexibility of the region reaching concept. In this novel
controller, a desired target is defined as a boundary instead of a point or region. For a
mapping of the uncertain restoring forces, a least-squares estimation algorithm and the
inverse Jacobian matrix are utilised in the adaptive control law.
To realise a new tracking control concept for a kinematically redundant robot, subregion
tracking control schemes with a sub-tasks objective are developed for a UVMS.
In this concept, the desired objective is specified as a moving sub-region instead of a
trajectory. In addition, due to the system being kinematically redundant, the controller
also enables the use of self-motion of the system to perform sub-tasks (drag
minimisation, obstacle avoidance, manipulability and avoidance of mechanical joint
limits).